Television synchronizing and control system



May 6, 194i. H. M. LEWIS TELEVISION SYNCHRONIZING AND CONTROL SYSTEM Filed Oct. 5, 1958.

INVENTOR RoLD M. Lawns ATTORNEY olllo lAu mohbmkuo Oll'o i nal.

Patented May 6, 1941y TELEVISION SYNCBBONIZING AND CONTROL SYSTEM l Harold M.,Lewis, Great Neck, N. Y., assigner to Hazeltine Corporation, a corporation of Dela- Application October 5, 1938, Serial No. 233,371

(Cl. P18-7.5)

Claims.

This invention relates to television receiving apparatus and more particularly to synchronizing and control systems for such apparatus. The invention is especially directed to the provision of a combined synchronizing-signal-separating and automatic amplification control system for television receivers.

In accordance with present television practice, a transmitted signal comprises a carrier wave modulated by light-modulation components representative of varying light values in successiveincremental areas of an image being transmitted and of its average background illumination, `and synchronizing-modulation components which correspond to initiations of successive lines and fields in the scanning of the image. The latter components ordinarily have amplitude values outside of the amplitude range of the lightmodulation components and extending in the direction of black. y

`At the receiver, a beam is so deflected as to scan and illuminate a, target in a series of fields of parallel lines. The synchronizing-modulation components of the received signal are utilized to control the scanning apparatus so as to synchro- `nize its operation with that of similar apparatus utilized at the transmitter in developing the sig- The intensity of the cathode ray is controlled by the video-frequency components of the received signal, as well as by the unidirectional background illumination voltage developed in the receiver, thereby to reconstruct the transmitted image.

Essential functions which must be performed ina television receiving system of the type described include deriving from the signal separate line-frequency and field frequency synchronizing pulses as Well as developing a, unidirectional-bias voltage representative of the average intensity of the carrier and independent of its light modulation and the utilization of this voltage automatically to control one or more operating characteristics of the receiver, for example, to effect automatic amplification control. Various methods have heretofore been devised for performing these functions but, in general, they have involved relatively complicated and/or unstable apparatus, or have otherwise left something to be desired.

It is an object of the present invention. to provide,` in a television signal-reproducing system wherein the received signal includes combined light-modulation components and synchronizingmodulation components having amplitude values outside the amplitude range of the light-modulation components, combined means for deriving from the received signal the synchronizing components separate from the other modulation components and a unidirectional control-bias voltage representative of the average intensity of the received. signal and independent of the llightmodulation components.

In accordance with the present invention, there 'is provided a television receiver adapted for reproducing a signal carrier having combined lightmodulation components and synchronizingmodulation components, the latter having amplitude values outside the amplitude range of the light-modulation components. The `receiver includes a rectifying device, means for deriving from a signal translated by said receiver a signal having components representingy the peaks of said synchronizing modulation components at a level corresponding to the unmodulated peaks of said carrier wave, and means for applying the derived signal to the rectifying device which includes means for maintaining the peaks of the synchronizing signals at the above-mentioned level to derive the synchronizing components separate from the other modulation components and a control effect, such as a unidirectional bias voltage, proportional to the average intensity of the received signal can'ier and independent of its light-modulation components. Means are further provided for utilizing the derived synchronizing components for synchronizing the operation of the receiver and for utilizing the control effect for controlling an operating characteristic of the receiver, for example, for automatic ampliilcation control. Apreferred embodiment of the invention includes a dioderectiiier for developing the bias voltage and impedance means connected in circuit with the same diode rectifier for deriving the synchronizing components.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims. I

In the accompanying drawing, Fig. 1 is a circuit diagram, partially schematic, of a cathoderay tube television reproducing system including circuits embodying the present invention; Fig. 2 is a group of curves representing certainoperating characteristics of the system of Fig. 1 to aid in the understanding of the invention; and Fig. 3 is` a circuit diagram illustrating a modified form of the invention.

ceiver of the superheterodyne type including an antenna system Ill-II connected to a radio-frequency amplifier I2, to which is connected, in cascade inthe order named, an oscillator-modulator I3, an intermediate-frequency amplier I4, a detector I5, a video-frequency amplier I6 and an image-reproducing device I1 which may be a cathode-ray signal-reproducing tube, these stages or units constituting the main signal-translating channel of the receiver. A line-frequency generator I8 and a held-frequency generatrlr I9 are also coupled to the output circuit of the amplifier I4, by way of synchronizing-signal-separating apparatus presently to be described, and to the scanning elements of the image-reproducing device II in the conventional manner. The stages or units Ill-I9 may all be oi' conventional wellknown construction so that detailed illustrations and descriptions thereof are deemed unnecessary herein.

'Referring brieily, however, to the operation of the system described above, television signals intercepted by the antenna circuit I-I I' are selected and amplified in the radio-frequency ampliiier I2 and supplied to the oscillatormodulator I3, where they are converted to intermediate-frequency signals which, in turn, are selectively amplified in the intermediate-frequency amplier I4 and delivered to the detector I5. The modulation components of the signal are derived by the detector I and are supplied to the video-frequency amplier I6 wherein they are amplified and from which they are supplied in the usual manner toa brilliancy-control element of the image-reproducing device I1.

The intensity of the scanning beam of the device I1 is thus modulated or controlled in acmicroiaradsv providing a. time constant of .00025 second. v

For the purpose oi deriving the synchronizing pulses separate from the other modulation pulses,

impedance means, speciiically, a resistor 29 may be included in series with the condenser 28 and the diode 2| as shown.l The resistor 29 is nf suchvalue as to have a relatively low impedance compared to that of the condenser 28 at the synchronizing frequencies. The input circuitsY of the line-frequency and held-frequency generators I8 and I9 are connected across the resistor 29 by way ofa suitable lead 30. Conventional circuits may be included in the generators I8 and I 9 for separating the line-synchronizing and field-synchronizing pulses from each other. The negative terminal of resistor 21 is connected, by way of a suitable Vfilter including series resistors 3l and shunt condensers 32 and conductors 33, to the control electrodes of one or more of the vacuum tubes included in the amplifier I2, oscillatormodulator I3, and amplifier I4, as shown.

vI'he operation of the system in accordance with the present invention may best be explained with reference to the curves of Fig. 2, in which curve A illustrates the load characteristics of the peak rectifier 2|, the abscissae representing applied alternating voltage and the ordinates representing the load current. The applied voltage, de-

rived from a signal translated by the receiver and having' signal components including the peaks of the synchronizing modulation components vat a level corresponding to the unmodulated peaks of the carrier wave, is illustrated cordance with the light-modulation voltages impressed upon the control element of the device I1 in the usual manner. Saw-tooth voltage or current .waves generated in the linefrequency and held-frequency generators I8 and I9, respectively, which are controlled by synchronizingvoltage pulses supplied from' the apparatus of this invention as presently to be explained, are applied to the scanning elements of the device I1 to produce electricscanning fields, thereby to deflect the ray in directions normal to each other so as to trace a rectilinear scanning pattern on the screen of the tube and thereby to reconstruct thev transmitted image.

Referring now more particularly to the portion ofthe system of Fig. 1 embodying the present invention, for the purpose of developing a control-bias voltage, there is provided a control signal-translating channel, .separate from the main signal-translating channel previously described, and comprising a vacuum-tube amplifier 20 and a rectifier device 2I connected in the order mentioned. The tube 20 may be of any suitable type having an input circuit comprising a coupling condenser 22 and leak resistor 23 connected to the output circuit of the ampliii'er I4. The output circuit of the tube 20 includles the primary winding 24 of a transformer 25, the

secondary winding 26 of which is coupled .to the diode peak rectier 2I provided with a load circuit comprising a parallel-connected resistor l2.1 and 'condenser 28 having a large time constant. This time constant should be considerably greater than. the period of the line-synchronizing pulses. For conventional systems utilizing, for example, 30 frames (60 fields) of 441 lines per second, the resistor 21 may be of the order of 500,000 ohms and the condenser 28 of the orderof 500 microby curve C, which shows the wave form of the envelope of the negatively modulated-carrier signal as developed inthe output circuit of the intermediate-frequency amplifier I4 and applied by way of the tube 20 and transformer 25 to the diode 2I. For the purpose` of simplicity, only a few line-frequency cycles are shown. The means for applying this signal to the diode 2| is also effective to maintain the peaks of the synchronizing modulation components at the above-mentioned level. The light-modulation components and synchronizing-modulation components are indicated at L and S, respectively, the latter, it will be noted, extending beyond the amplitude range of the former. Signal levels corresponding to white and black are indicated inthe iigure at W and B, respectively.

It will be seen that the peak rectier 2| passes current only during the occurrence of synchronizing pulses, which represent the peak values of the modulated-carrier wave on one side of its axis, this being determined by the largetime constant circuit provided by the resistor 21 and condenser 28. There is thus built up across the load l circuit 21, 28 a unidirectional voltage, illustrated tion components.

at e in Fig. 2,*which signal. is proportional to the maximum amplitude of the carrier wave and independent of light-modula- The filter comprising the resistors 3| and condensers 32 serves to remove residual iiuctuations from the rectified voltage and the resultant steady unidirectional bias voltage is impressed negatively on the control grids of is the peak-rectied applied one or more of the tubes in the stages I2, I3 and I4 to control the amplification of these stages inversely in accordance with the maximum value of carrier-Wave amplitude and independently of light-modulation components. signal intensity of the main channel is maintained within a Thus, the output signal-translating relatively narrow That is, the average value of this voltage 2,240,507' range for a wide range of received signal inten-A sities. Since the diode 2i passes current only during the occurrence oi the. synchronizing pulses, representing the charging current of, condenser 18, this current` ilows through the resistor 29,

which is in series with the diode, and there are thus developed across thisresistor synchronizing pulses iree from the light-modulation components of the signal, as illustrated by curve i of Fig. 2L These pulses are applied to the generators |8` and lsv in which conventional separating apparatus serves to separate the line-synchronizing and .field-synchronizing.` pulses from each other and these pulses are. utilized to maintain the `generators I8 and `I9 in synchronism with the corresponding apparatus -at the transmitter, in the usual manner.

nents separate from said other modulation components and a control effect proportional to the i l intensity of said carrier wave and independent oi light-modulation components, means for uti-- i plitude values outside the amplitude range' of The single 4rectifying circuit described above thus serves to derive from the signal both a unidirectional biasvoltage proportional to the intensityof the modulated-signal'carrier and independent of its light-modulation components and the synchronizing-modulation componentsl separate from the othermodulation components.

Fig. 3 shows a` diode Vrectiiier arrangement which may be substituted for that shown in Fig. l... Here thearrangement is the same as in Fig. l except that resistor`29 is connected betweenl the diode cathode and its load circuit rather than in its load circuit.- Theoperation of this arrangement is substantially `the -same as, that of Fig. 1. It is to be noted that theA control system of the present invention may be energized v'vith` the detected signal as well as the modulated-carrier signal. In that case. theinput circuit of rectifierilZI may be directly connected, that is; conthe light-modulation components comprising, a

main` signal-translating channel, a separate control signal-translating channel, means for applying a signal translated by said receiver and having components -representing the peaks of said synchronizing-modulation components at a level corresponding to the unmodulated peaks of said carrier wave to both of said channels, a recnected by a direct current connection, to the output circuit of the detector instead oi.' the amplier I4 and the detected modulation-signal envelope, that is; the envelope of half the wave. s C shown inFig, 2, is impressed on the diode rectier 2i. The operation is otherwise the same as that described above. In other words, an essential feature oi the arrangement of the invention is` that the signal rectifying means be energized by a sign-al translated by the receiver and having components representing the peaks of the corresponding to the unmodulated peaks of` the received signal-carrier wave.

,While there have been described what are at present considered to be the preferred embodiments of` this invention, it will be obvious to those4 skilled in the art that various changes and modifications may be made therein without departing fromthe invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention. i I

What is claimed is:

i 1. A television receiver ladapted'to reproduce a signal-carrier wave having combined lightmodulation components and synchronizing-modulation components "having amplitude values outside the amplitude range of a light-modulation components comprising, a rectifying device. means for deriving from a signal translated by said receiver a signal having components representing the peaks oi said synchronizing-modulation components at a level corresponding to the unmodulated peaks of said carrier wave, means for applying said derived signal'to said device including `means for maintaining said peaks at said level to derive said synchronizing compotsynchronizing-modulation components ataI level f vtifying device included in said control channel,

means for applying said signal applied to said Hcontrol channel to said device including means for maintaining said peaks at said level to derive said synchronizing components separate from said other modulation components and a control eiTect proportional tothe peak intensity of said carrier wavek and independent of llight-modulation components, means for utilizing said control eiect for controlling an operating characteristic of said main channel, and means for 'utilizing said separated `synchronizing compolated by said receiver and having components representing the peaks of said synchronizingmodulation-components at a level corresponding to the unmodulated peaks of said carrier wave to'.

both of said channels, a rectifying device ineluded in said control channel, means for apply-j ing said signal applied to said control channel -to said device including means for maintaining said peaks at said level to derive a control-bias voltage proportional to said peak value Vof said carrier wave and to develop from said signal said synchronizing components separate from the other modulation components, means `ior utilizing said control-biasl voltage for controlling an operating characteristic of said main channel, and means for utilizing said separated synchronizing components for synchronizing the operation of the receiver.

` 4. A television receiveraclapted for the reception of a television signal-carrier wave modulated negatively by light components and modulated by synchronizing components having amplitude values outside the amplitude range of the light components, `a rectifying device, means for deriving from a signal translated by said receiver a signal having` components representing the' peaks of said synchronizing-modulation components at a level corresponding to the unmodulated peaks of said carrier Wave, means for applying said derived signal to said device including means for maintaining said peaks at said regeiver adapted to reproduce a` ,modulation components and level to derive a control-bias voltageA proportional to the peak value of said carrier on one side of its axis and to derive said synchronizing components separate from said yother modulation components, means for utilizing said control-bias voltage for controlling an operating characteristic of the receiver, and means for utilizing said separated synchronizing components for synchronizing the operation of the receiver.

5. A television receiver adapted for the reception of a television signal-carrier Wave modulated negatively by light components and modulated by synchronizing components having amplitude values outside the amplitude range of the light components, a main signal-translating channel, ay separate control signal-translating channel, means for applying a signal translated by said reeciver and having components representing the peaks of said synchronizing-modulation components at a level corresponding to the unmodulated peaks of said carrier wave to both said channels,` a rectifying device included in said control channel, means for applying said signal applied to said control channel to said device including means for maintaining said peaks at said level to derive a control-bias voltage proportional to the peak value of said carrier on one side of its axis and to derive said synchronizing components separate from said other modulation components, means for utilizing 'said control-bias voltage for controlling an operating characteristic of said main channel, and means for utilizing said separated synchronizing components for synchronizing the operation of the receiver.

6. A television receiver adapted to reproduce a signal-carrier wave having combined lightmodulation components having amplitude values outside the amplitude range of the light components, said wave having a wide range of sigsynchronizingcarrier wave, means for applying said derived signal to said device including means for maintaining said peaks at said level to derive a control bias voltage proportional to the intensity of said carrier independent of light modulations and to derive said synchronizing components separate from the other modulation components, means for utilizing said control-bias voltage for maintaining the intensity of the signal output of said main channel within a relatively narrow range for a Wide range of received signal input intensities, and means for utilizing said synchronizing components to synchronize the operation of the receiver.

8. A television receiver adapted to reproduce a signal-carrier wave having combined lightmodulation and synchronizing-modulation comnal-input intensities, comprising, a. rectiiying device means for deriving from a signal translated by said receiver a signal having components representing the peaks of said synchronizingmodulation components at a level corresponding to the unmodulated peaks of said carrier wave, means for applying said derived signal to said device including means for maintaining said peaks at said level to derive a control-bias voltage proportional to the intensity of said carrier Wave and independent of light-modulation components and to derive said synchronizing components separate from the other modulation components, means for utilizing said control-bias voltage for maintaining the intensity of the signal output of said receiver within a relatively narrow range for a wide range of received signal input intensities, and means for utilizing said synchronizing components to synchronize the operation of the receiver.

7. A television receiver adapted to reproduce a signal-carrier wave having combined lightmodulation components and synchronizing-modulation components having amplitude values outside the amplitude range of the light components,

said Wave having a wide range of signal-input intensities comprising a main signal-translating channel, a separate control signal translating channel, a rectifying device, means included in said control channel for deriving from a Signal translated by said receiver a signal having components representing the peaks cf said synchronizing-modulation components at a level corresponding to the unmodulated peaks of said ponents having amplitude values outside the amplitude range of the light-modulation components, comprising, a diode rectifier, means for deriving from a signal translated by said receiver a signal having components representing the peaks of said synchronizing-modulation components at a level corresponding to the unmodu lated peaks of said carrier wave, means for applying said derived signal to said device including means for maintaining said peaks at said level to derive a control-bias voltage proportional to the intensity of the carrier wave and independent of its light-modulation components, impedance means in circuit with said rectiier for deriving from said signal synchronizing components separate from the other modulation components, means for utilizing said control-bias voltage for controlling an operating characteristic of the receiver, and means for utilizing said separated synchronizing components for synchronizing the operation'oi the receiver.

9. A television receiver adapted to reproduce a signal-carrier Wave having combined lightmodulation and synchronizing-modulation cornponents having amplitude values outside the amplitude range of the light-modulation comnents, comprising a diode rectier having a load circuit including a resistor and condenser connected in parallel and providing a time constant circuit, means for deriving from a signal translated by said receiver a signal having components representing the peaks of said synchronizing-modulation components at a level corresponding to the unmodulated peaks of said carrier Wave, means for applying said derived signal to said device including means for maintaining said peaks at said level to derive a controlbias voltage proportional to the intensity of the carrier wave and independent of its light-modulation components, a" resistor connected in series with said diode and said condenser for deriving from said signal synchronizing components separate from the other modulation components, means for utilizing said control-bias voltage for controlling an operating characteristic of said receiver, and means for utilizing said separated synchronizing components for synchronizing the operation of the receiver.

l0. A television receiver adapted to reproduce a signal-carrier wave having' combined lightmodulation and synchronizing-modulation components having amplitude values outside the amplitude range 'of the light-modulation components, comprising a main signal-translating channel, a separate control signal-translating lation components at a level corresponding to the' unmodulated peaks of said carrier wave to said channels, a diode rectifier included in said control channel, means for applying said signal applied to said control channel to said device including means for maintaining said peaks atsaid level to derive a control-bias voltage proportiona1`to the peak value of said signal-carrier wave on one side of its axis, impedance means in circuit with said rectier' for deriving from said signal synchronizing components separate from thje other modulation components. means for utilizing said control-bias voltage for controlling an operating characteristic yo1 the receiver, andFV means for utilizing said separated synchronizing components for synchronizing the operation of the receiver.

HAROLD M. LEWIS. 

